Field of the Invention
The present invention relates to an optical device comprising an encoder detecting a position of an object to be measured.
Description of the Related Art
An optical device such as an interchangeable lens mounted on an image pickup device comprises a lens driving mechanism unit that moves a focusing lens and a variable power lens constituting an optical system in the direction of an optical axis. The lens driving mechanism unit is provided with an encoder for detecting a position of the lens. A configuration of such a lens driving mechanism unit having an encoder is disclosed in Japanese Patent Laid-Open No. 2014-35438. The lens driving mechanism unit of Japanese Patent Laid-Open No. 2014-35438 comprises a base part, a cylinder part that is rotatable relative to the base part in a circumferential direction, and at least three support parts that rotatably support the cylinder part with respect to the base part. A coupling unit provided for the cylinder part, a scale part mounted on the cylinder part, and a detecting part detecting a position of the cylinder part relative to the base part using the scale part are disposed. In the configuration of this lens drive system, the positions of the coupling unit and the detecting part are symmetrical with respect to the center of the cylinder part, and overlap each other in the direction of the optical axis. Thereby, space efficiency is improved.
In the related art, due to unnecessary motion of the cylindrical member within a backlash in the direction of the optical axis, for the purpose of avoiding a drop in detection precision of the position detecting encoder, the cylindrical member is required to be pushed in the direction of the optical axis by a pressing leaf spring without a backlash. For this reason, components called a pressing spring, a slip ring, and a differential roll are needed, and the number of components increases.